2
$\begingroup$

In the derivation of Bernoulli's equation through conservation of energy, as shown in http://www.4physics.com/phy_demo/bernoulli-effect-equation.html, the net work done on a section of fluid is calculated and equated to the change in its mechanical energy. According to the site, two forces do work on the fluid; namely, an external force $F_1$ driving the fluid forward, and a force $F_2$ exerted at the right end of the fluid. How is the force $F_2$ exerted on the fluid, and why is it directed opposite to the motion?

$\endgroup$

1 Answer 1

2
$\begingroup$

The forces are provided by the pressure of fluid further on. The force $F_1$ is caused by the pressure of the fluid 'behind' the body of fluid considered, the force $F_2$ is caused by the fluid 'ahead' pushing back. Pressure is an internal force for a fluid, any surface within a fluid volume will have the force of pressure acting across it.

$\endgroup$
1
  • $\begingroup$ Right. It's just F=ma for an infinitesimal volume. And F=ma conserves both momentum and kinetic energy. $\endgroup$ Commented Nov 29, 2017 at 16:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.